1. Field of the Invention
The present invention relates to an electronic apparatus and, more particularly, to an electronic apparatus having a memory for storing data to be backed up when an unexpected power trouble occurs.
2. Related Background Art
Conventionally, techniques of backing up data when a power trouble such as an unexpected power failure occurs have been used in a variety of electronic apparatuses.
For example, in apparatuses such as a facsimile apparatus and a digital composite machine integrating a facsimile function and a printer function, data stored in an image memory is backed up to prevent erasure of received images and data of images reserved for transmission when a power failure occurs. In this type of communication apparatuses, data for controlling and managing communication, e.g., telephone number data and communication recording logs (so-called communication management data such as communication time, required time, and communication results), are also backed up.
As a means for backup, data to be backed up may be stored in a hard disk. However, backing up a memory such as a DRAM by using a secondary battery (an NiCd battery, lead battery, vanadium-based lithium battery, or another chargeable battery) which is more advantageous in cost and installation space, is extensively used.
A similar backup power supply is also used to drive a real-time clock. This configuration can also be considered to back up count data of the real-time clock and hence can be regarded as a backup system.
In a system using a secondary battery described above for memory backup, deterioration of this secondary battery is a serious problem.
Generally, deterioration of chargeable batteries used as secondary batteries of this sort accelerates at high temperatures and further accelerates when a cycle of charging and complete discharging is repeated.
When the life of a secondary battery has expired, the purpose of memory backup cannot be achieved, and a user may lose important data.
In many conventional apparatuses, during a period in which the main power supply is OFF, a secondary battery backs up a memory such as a DRAM. While the main power supply is ON, this secondary battery is charged by a charging circuit.
Since the memory size of an image memory of a facsimile apparatus or a digital composite machine is large, the memory can usually be backed up for about five hours at most when charging and backup are performed as described above (when no charging is performed in a period during which the main power supply is OFF).
When the main power supply of an apparatus is turned off every night (or when an apparatus is used in a similar way, e.g., when the main power supply of an apparatus is turned off for a predetermined period of time on the basis of timer counting), deterioration of a secondary battery may make the conventional system as described above unable to achieve its original function of backing up data if power is shut down by a sudden power failure or the like.
To prevent this, it has been considered to monitor the voltage level of a battery constituting a secondary battery, estimate the degree of deterioration from a voltage drop, and, if necessary, allows a user or a serviceman to replace the battery itself with a new one.
Even if such a countermeasure is used, however, a battery deteriorates very rapidly when a charge-complete discharge cycle is repeated. In effect, when the power supply is turned off every night, the battery must be frequently replaced. Therefore, this countermeasure is not a realistic solution.
In this sense, to prevent deterioration of a secondary battery, it is important to reduce the number of repetition times of a charge-complete discharge cycle.
Depending on the type of data, it is necessary to reconsider whether the data is to be backed up by using a resource, i.e., a secondary battery, having the problem of deterioration as described above. For example, data such as telephone number data and communication logs of a facsimile apparatus or a composite digital machine must be backed up because the user should be in trouble if they are lost. However, image data received in a memory but still unrecorded can be forcedly output if power shutdown is unavoidable. This obviates the need for backup using a secondary battery.
Thus, there is thought of such a structure that which in linkage with a main switch for controlling turn-on/turn-off of a main power supply of an apparatus, supplying of a power from a backup battery to a memory (that is, discharge of the backup battery) to thereby reduce the number of cycles of charge/discharge of the backup battery.
Alternatively, there may be a case where such a structure is more practical that the premise that data stored in a memory is always important and it must be backed up at all times is withdrawn, and as the need arises, a user can shut down a main power supply of an apparatus or a backup power supplying system.
The present invention aims at removal of the above-mentioned troubles to thereby protect important data stored in a memory and practically control the supply of an electric power in an apparatus equipped with a main power supply or a backup power supplying system.